It was reported that removing the certificate from the System.Windows.Controls.Layout.Toolkit assembly was still not solving the issue, therefore I tried the steps outlined in the previous blog post and my experience was as follows :-

1. The particular powershell script was not running - In the blog post it details that I had to run the "set-executionpolicy remotesigned" command however I also had to unblock the script file which also meant changing the permissions for that file for my particular user on my machine to allow this unblock to occur.

2. Once the assemblies certificate had been removed, the problem reported in the forum post was still occuring so had a look at the Bin directory of the particular project I was using and there were two other DLLs from the Toolkit :-System.Windows.Controls.Toolkit.dllSystem.Windows.Controls.Toolkit.Internals.dll

These other two DLLs also needed their certificates removing. After doing so, I then had to reference these additional two assemblies directly in my project so that they would be the versions that were used (originally I had only referenced the System.Windows.Controls.Layout.Toolkit assembly). After doing this I am now able to test the page transistion sample.